The studies proposed in this research grant will examine several techniques for restoring neural function in animals with experimentally- induced neurodegenerative disorders -- in particular, animals with experimental Parkinson's disease. The pharmacological interaction between antiparkinsonian drug therapy [e.g., levodopa] and the development of dopaminergic neurons will also be examined in grafted and intact dopaminergic systems. During the last decade, basic scientific research has provided encouraging evidence that neurons from embryonic donors can be successfully transplanted into the brain of adult recipients. Using embryonic neurons to replace degenerating neurons may provide salutary effects in several diseases associated with the senescence of the nervous system, including Parkinson's and Alzheimer's diseases. Previous neural grafting studies have shown that embryonic dopamine neurons survive transplantation and release dopamine (DA) into the brain parenchyma of animals with experimental parkinsonism, however, fiber outgrowth from those cells is often limited to the immediate vicinity of the graft. More extensive outgrowth is desirable for promoting and maintaining functional recovery of damaged neural systems in animal models as well as human neurodegenerative disorders. Fiber outgrowth of grafted neurons can be extended when embryonic DA neurons are simultaneously co-grafted with their embryonic target cells. The proposed studies are intended to further examine the trophic effect embryonic striatal cells may exert upon grafted or damaged DA neurons using (1) morphological techniques to examine enhanced fiber outgrowth from dopaminergic grafts and (2) neurochemical techniques [in vivo microdialysis] for measuring levels of DA release in co-grafts versus single DAergic grafts. Second, dopamine cells of the nigrostriatal pathway are the most profoundly affected locus of nerve cells in idiopathic Parkinson's disease. The nigrostriatal pathway consists of DAergic cell bodies located within the midbrain that give rise to long axonal projections that course rostrally and terminate at a distal forebrain target site, the striatum. Most of the DA synthesized by these cells is transported and released into striatum, therefore neurodegeneration of these cells results in an extreme loss of the striatal DA. Moreover, there is biochemical, morphological, and neuropharmacological evidence that DA is released in the vicinity of the cell bodies [midbrain] an modulates neural function and affects motor behavior. To date, the vast majority of transplantation studies have focused on restoring DA function in the striatum in order to reverse motor dysfunction; they have not addressed the issue of how DA losses in the midbrain might also affect motor function. The proposed studied intend to examine functional, morphological, and neurochemical changes that occur after neural transplantation of embryonic DA neurons into both the midbrain and forebrain sites of animals with experimentally-induced parkinsonism. Third, recent studies examining the combined treatment of neural grafting while maintaining antiparkinsonian drug therapy suggest that levodopa treatment may interfere with the salutary effects of neural grafts and may even impair the development of grafted DA neurons. These studies were performed in animals of hemiparkinsonism and the effects of levodopa on the function of the intact striatum complicate the interpretation of these data. Therefore, in order to more fully understand this phenomenon and to further characterize it, bilateral grafts of embryonic DAergic tissue will be implanted into the DA-denervated striata of animals with bilateral lesions of the nigrostriatal pathway and graft morphological development, motor function, and neurochemical characteristics of grafted embryonic DA neurons will be assessed. In a complimentary study, the effects of levodopa on the developing nigrostriatal system will also be characterized using immunocytochemical techniques.